Drawbar support for leveling circle frame on road graders

ABSTRACT

A linkage adjacent the normal ball joint of the drawbar of a road grader which permits leveling of the circle frame, regardless of the depth of cut of the grader blade throughout the normal range of grader blades on road graders.

United States Patent [191 [111 3,856,089

Rivinius Dec. 24, 1974 [54] DRAWBAR SUPPORT FOR LEVELINC 3,376,9374/1968 Grober 172/679 X CIRCLE FRAME 0 O GRADERS 3,454,109 7/1969Roberts 3,595,320 7/1971 Mittelstadt 172/781 Inventor: TheodoreRivinius, 810 N. 2nd St.,

Bismarck, N. Dak. 58501 Filed: Sept. 20, 1973 Appl. No.: 398,947

Related US. Application Data Continuation-in-part of Ser. No. 267,434,June 29, 1972, abandoned.

US. Cl. 172/4.5, 172/789 Int. Cl E02f 3/76 Field of Search 172/789, 779,780, 781,

References Cited UNITED STATES PATENTS 8/1966 Olafson 172/780 PrimaryExaminerStephen C. Pellegrino Attorney, Agent, or Firm-Dugger, Johnson &Westman [57] ABSTRACT A linkage adjacent the normal ball joint of thedraw bar of a road grader which permits leveling of the circle frame,regardless of the depth of cut of the grader blade throughout the normalrange of grader blades on road graders.

13 Claims, 9 Drawing Figures PATENTEUUECZMQM DRAWBAR SUPPORT FORLEVELING CIRCLE FRAME ON ROAD GRADERS CROSS REFERENCE TO RELATEDAPPLICATION This application is a continuation-in-part of my copendingapplication Ser. No. 267,434, filed June 29, 1972, now abandoned, forDrawbar Support for Leveling Circle Frame on Road Graders.

BACKGROUND OF THE INVENTION Field of the Invention The invention relatesto improvements in earth working graders and more particularly to asupporting framework for leveling the circle frame with respect to ahorizontal fore and aft line regardless of the depth of cut of the bladethat is carried by a circle frame of a road grader. This also means thatthe plane of the circle frame is kept parallel to the plane of the cutby the blade as the grader moves forwardly. For example, in my US. Pat.No. 3,421,589, issued Jan. 14, 1969, a four bar lifting link is used forsupporting the circle frame in a parallel relationship to a horizontalfore and aft line regardless of the depth of cut of the circle frame,and maintaining this parallel relationship of the circle framethroughout the range of operation of the circle frame. The circle framedrawbar in my aforementioned patent is connected to the circle framethrough hinged joints that permit the circle frame to be independentlysupported on its lift links to keep the circle frame parallel to ahorizontal, fore and aft extending line while being pulled along by thedrawbar in a normal manner.

In addition, US. Pat. No. 2,941,319, issued on June 21, 1960 to Beemeret al. shows a parallel linkage for supporting the circle frame, andtaking the place of the conventional drawbar. The parallel linkage issubject to wear at several pivot points, and in a high load situationsuch as that with a road grader drawbar these inaccura cies due to wearin a linkage can cause unsatisfactory operation.

In graders where the circle frame is not maintained parallel to ahorizontal, fore and aft line, if the blade is rotated about its uprightaxis, the angle of cut will change and this requires additionaladjustment. In addition, if automatic leveling or slope controls areused, the automatic system will not adjust because the sensing device isusually sensitive to the transverse angle of the circle frame and nocorrection would be made unless special compensation techniques areemployed.

SUMMARY OF THE INVENTION The present invention relates to a simpleconnecting linkage between the normal ball joint of a drawbar of a roadgrader and the frame of a road grader which can be adjusted to keep thecircle frame parallel to a horizontal, fore and aft line (or a lineparallel to the direction of travel) at a particular depth of cut of theroad grader blade carried by the circle frame. The linkage can beadjusted to keep the plane of the circle frame parallel to the plane cutby the blade as the grader moves along the ground. The linkage also canbe made so that it will automatically compensate for changes in depth ofcut of the circle frame, or it can be manually adjusted, in one form ofthe invention, to insure that the circle frame is parallel to ahorizontal, fore and aft line at one particular depth of cut of thegrader blade. When the circle frame is parallel to a horizontal, foreand aft line, the blade may be rotated about its upright axis withoutchanging the transverse angle of cut of the blade, or slope of cut.

For finishing work in building roads and the like, a particular depth ofcut is desired and the transverse angle of grade is controlled. Theimportant point is that if the circle frame is parallel to a horizontalline in fore and aft direction (the direction of movement of thegrader), the blade can be rotated about the upright axis of the circleframe without changing the transverse angle of the grade being cut.Without the parallel relationship of the circle frame to a horizontalfore and aft line, one end of the blade will dig in more than the otherwhen the blade is rotated about its upright axis.

The linkage as shown comprises a short link member connected to thenormal drawbar ball joint, and also connected in turn to the circleframe drawbar about a substantially transverse, horizontal axis. Theangular position between the link and the drawbar is maintained througha lever arrangement and an adjustable retaining device such as a screwor a hydraulic cylinder, so that the angular position of the drawbar andthe link can be adjustably fixed. The angular position of the forwardend of the drawbar relative to the ball joint, and this in turndetermines the fore and aft elevation of the plane of the circle framein relation to the horizontal.

For precise control, a depth servo mechanism using a parallelogramprinciple is also shown. The movement of the earth working blade changesthe arrangement of a linkage which, in turn, actuates a potentiometer todrive a servo valve, and adjust the hydraulic cylinder or power meansuntil the drawbar returns to a null or level position.

The device is simple to make, and relatively low in cost in install andmay be used as a modification kit for existing graders. The position ofthe link can be automatically adjusted when a hydraulic cylinder is usedin response to changes in depth of the grader blade.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of atypical road grader showing a drawbar made according to the presentinvention installed thereon;

FIG. 2 is a side elevational view of a forward portion of the drawbar ofthe grader of FIG. 1 showing the linkage used with the presentinvention;

FIG. 3 is a sectional view taken as on line 33 in FIG. 2;

FIG. 4 is a side elevational view of a portion of the linkage shownremoved from the grader for illustrative purposes;

FIG. 5 is a side elevational view of a modified form of the inventionshowing the unit in a lowered position relative to the other views;

FIG. 6 is a fragmentary side elevation view of a front portion of a roadgrader having a parallelogram link depth change sensor for control of alinkage made according to the present invention;

FIG. 7 is an enlarged side view of the depth change sensor and linkageof FIG. 6;

FIG. 8 is a side view of the device of FIG. 7 in a second operationalposition; and

FIG. 9 is a bottom plan view of the device of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A road grader illustratedgenerally at 10 includes a main frame 11 that is of the usual orpreferred design, and the main frame is supported at the forward endwith steering wheels 12, and at the rear portion with power drive wheels13. The operators platform 14 is positioned so that the operator canreach suitable controls 15 for controlling the road grader and thegrader blade on the grader. An engine housing 16 houses an engine ofusual design for powering the road grader and moving it along a groundsurface 17 for use. The road grader as shown includes a steeringassembly 18 for steering the steering wheels 12, and power lift devices19 of the usual design controlled by the controls in the operatorsplatform 14 for raising and lowering a cutting blade assembly 22. Thecutting blade assembly 22 is of the usual design as well, and includes agrader blade 23 that engages the ground 17 for making the grader cut,and this grader blade 23 is mounted on suitable supports 24 to a circleframe 25 that is rotatable about an upright axis with respect to acircle frame support 26. The circle frame support 26 is in turn attachedto a drawbar 27. This construction is all conventional in road graders,and is not gone into in detail in this specification.

The power lift mechanisms 19 (there is a separate lift mechanism on eachside of the grader) in turn drive rotatable shafts 30 of usual design,that are mounted in bearings 31 on the main frame 11, and have controlarms 32 mounted thereon. Lift links 33 are attached to the arms 32, andalso are attached as at 34 to a cross member 35 on the rear portions ofthe drawbar. There are lift links on each side of the grader so that atransverse slope can be established for the grader blade. The linksraise or lower the sides of the circle frame when the particular shaft30 and arm 32 for that lift link is rotated. A link 36 also may beprovided for moving the circle frame and grader blade 23 laterally fromside to side with respect to the main frame if desired. Because the liftlinks, control shafts 30 and arms 32 are conventional, they are notshown in detail.

The drawbar 27 is modified over a conventional device in order tomaintain the fore and aft axis of the circle frame 25, about which thecircle frame tilts, parallel to the horizontal regardless of depth ofcut of the grader blade 23. It can be seen that by rotating the shaft 30in a conventional manner, the link 35 will be raised or lowered, and thecorresponding side of the circle frame will also be raised or loweredbecause of the cross member 35. When the controls for the blade arecontrolled automatically to maintain a preselected slope to the blade,it is highly desirable that the grader blade can be rotated about theupright rotational axis of the circle frame. Any changes of the graderblade 23 about its upright axis in a conventional blade drawbar mountingwill result in a different slope of cut of the blade without changingthe setting of the circle frame, and consequently where the fore and aftaxis of the circle frame is not maintained parallel to the cut left bythe grader as the grader moves, automatic operation of the slope controlis difficult.

In the present device, a relatively simple linkage arrangement isadvanced for insuring that the fore and aft, central axis of the circleframe, which is indicated at 40, will be maintained as a horizontalaxis. This also can be stated that the plane of the circle frame isparallel to a fore and aft extending horizontal line. In this particularform of the invention, a coupling link indicated generally at 41 isprovided for coupling the forward end of the drawbar 27 to the mainframe 11. The main frame 11 has a downwardly depending forward portion42 that mounts a ball housing 43 for rotatably mounting a spherical ball44 (see FIG. 3). The use of a ball joint at the forward end of thedrawbar is conventional, and the conventional drawbars use ball jointsso that the conventional graders have ball joints at the forward ends ofthe drawbar in order to insure that the drawbar can move up and down orside to side in accordance with the controls from the grader.

In this particular instance, however, the ball 44 is attached to a link45 that extends rearwardly and is fixed to a block 46A which has a pairof stub shafts 46,46 extending laterally therefrom. The line 45 isrelatively short in length, and the stub shafts 46,46 are rotatablymounted in suitable bearings 47,47 positioned in the legs of abifurcated end portion 48 of the drawbar 27. This bifurcated end portionis formed by a recess 49 defined in the end of the drawbar.

The assembly further includes a lever assembly 51 that is fixedlyattached to the block 45A as shown in FIG. 4, and this lever assembly 51comprises two spaced arms that project upwardly from the link assembly.It can be seen that the link assembly is made by passing the ball jointshaft 45 through the block 45A thereon and attaching the shaft 45 with asuitable nut so that the unit is clamped together as a rigid link.

The angular position of shafts 46 with respect to the bifurcated end ofthe drawbar 27 is controlled with an adjustable member acting betweenthe lever arms 5] and the drawbar 27. As shown, the lever arms 51 have arod end 53 attached thereto with a pin. The rod end 53 is connected toan extendable rod of a hydraulic cylinder 54. The base end of thecylinder 54 is attached to a suitable bracket 55 which is fixed to thedrawbar 27. The hydraulic cylinder 54 is controlled through a suitablevalve from a pressure source, and by extending or retracting the rod 55,the angular position between the link 45 and the drawbar is changed. Forexample, in position shown in FIG. 1 the link 45 is shown extendingdownwardly from the drawbar and when the rod 55 is retracted, the leverarms 51 would be moved to a dotted line position as shown in FIG. 2, andthe drawbar 27 would lower to its dotted line position shown in FIG. 2with respect to the ball joint. This means that if the grader blade 23was making a deep cut, the fore and aft axis 40 of the circle frame canbe leveled with respect to a horizontal plane by adjusting the hydrauliccylinder 54 to retract the rod 53 and move the lever arms 51 to thedotted position shown in FIG. 2. The amount of movement would, ofcourse, depend upon the depth of cut of the blade 23.

If desired, the position of the hydraulic cylinder 54 can beautomatically controlled by mounting a sensor switch on the cross member35. The sensor 60 can be a microswitch that senses the angle between thecross member 35 and the line 33, because when the circle frame is raisedor lowered by operating the near link 33, and assuming the transverseangle of the blade does not change, the angle between the link and thecross member 35 will change. The sensor 60 could also be used in otherlocations to sense depth changes. Thus, if the depth sensor 60 controlsthe valve from the hydraulic cylinder 54, the sensor 60 would cause thecylinder to be actuated to a desired position, depending on whether theblade is raised or lowered. The controlled valve directs fluid underpressure to the cylinder 54 until the sensor 60 reaches a null orpreselected point, at which position the drawbar would again be inproper relationship with respect to a horizontal plane so that the foreand aft axis 40 would be parallel to a horizontal plane and the circleframe would be properly positioned. The valve for the cylinder alsocould be manually'operated and manually adjusted when the blade depthwas adjusted.

However, if one particular depth of cut is going to be made, theadjustment member does not have to be automatically operated but can bemerely manually operated and adjusted to achieve the desired result atthe desired depth of cut. It should be noted that one of the shafts 46can have an indicator needle 61 attached thereto and this indicator 61can be used in relation to a depth scale 62 on the drawbar to indicatethe blade depth for which the link is set to obtain parallelrelationship of the axis 40 to a horizontal plane. This is a visualindicator that could be used with a manual adjustment device if desired.

FIG. 5 illustrates a manual adjustment device that can be used betweenthe drawbar 27 and the lever arms 51. In this particular instance ascrew member 65 has a head 66 that is held between the levers 51 with asuitable pin 67, and a pair of nuts 68 are provided on opposite sides ofa spherical ball member 70 that is mounted in a bracket 72 that isattached to the drawbar 27. Member 70 is used to provide properalignment and bracket 72 has a part spherical seat for the member 70. Byadjusting the nut 68 properly, the angular position of the link 45 canbe changed to raise and lower the front of drawbar 27 a desired amount.In this particular instance, the indicator needle 61 has a veryimportant function because the adjustment takes place manually byadjusting the nuts 68 and the indicator is used to show when the properadjustment has been made for the depth of cut that is desired to be madewith the grader.

Referring to FIGS. 6 through 9, a modified form of the invention isshown with a different type of device for sensing changes in elevationor depth of the circle frame blade. The device of FIGS. 6 through 9 isdesigned primarily for use with servo valve controls for operatinghydraulic cylinders to control the various mechanisms of the graderincluding the blade depth control and the like, although the system ofFIGS. 6 through 9 can be used with the previously described mechanicalform of the invention as well.

Referring specifically to FIG. 6, the forward portions of the roadgrader are shown. The forward portion 42 of the main frame 11 has theball housing 43 thereon. A grader circle frame drawbar is constructedsubstantially the same as in the previous form of the invention and isindicated at 75. The drawbar is used for mounting the circle frame inthe same manner as previously described, and the circle frame alsomounts the grader blade. The circle frame is raised and lowered byhydraulic cylinders, or other conventional raising and loweringmechanisms.

A ball member 76 is mounted in the socket 43, and a stub shaft 77 ismounted onto this ball member. The

stub shaft 77 is constructed just as the shaft 45 is, and to a centerblock having an upright lever 78 thereon which is used for controllingthe angular position between the stub shaft 77 and the drawbar 75. Thecenter block of stub shaft 77 has a pair of outwardly extending shafts79 thereon which are rotatably mounted in bearing housings 80 that inturn are attached to the forward portion of the drawbar 75 with suitablebolts and coupling members.

A hydraulic cylinder 83 is mounted onto the drawbar 75 with a suitablesupport member 84, and has an extendable and retractable rod 85 that isconnected through a rod end member and pin 86 to the lever 78. Thehydraulic cylinder 83 is controlled through an electro-hydraulic servovalve 87, and the hydraulic circuit includes a pump 88 and a suitablecontrol for the servo valve. As shown, a null center potentiometer orvoltage divider 89 is suitably connected so that at a neutral positionthe servo valve is in a neutral position. If the potentiometer movesaway from its center or null position the servo valve will operate tomove the cylinder to extend or retract, depending on which way thepotentiometer moved. Operation of cylinder 83 results in raising orlowering of the forward end of the drawbar 75 so that the circle framewill be leveled in the same manner as previously described.

The servo valve 87 is controlled through the potentiometer 89 from asuitable power source and the potentiometer may be connected through avalve amplifier 82 to the servo valve, the controls are set so that thepotentiometer is at a null position when the circle frame is leveledwith respect to the ground surface. In order to sense deviations of thecircle frame drawbar 75 from its level position, a parallelogram linkageis used. A pivot tube 92 is welded to one of the bearing housings 80, asshown in FIG. 7 (see also FIG. 9 which is the bottom view). This pivottube 92 in turn rotatably mounts a pin 93 which has a lever arm 93Aattached thereto. The lever arm 93A extends underneath the bearingmounting members 80, back toward the centerline of the machine, as shownperhaps best in FIG. 9 A link 94 has a rod end 95 with a sphericalbearing therein which is attached in a suitable manner to the outer endof the lever 93A. The link 94 in turn extends forwardly toward the ballsocket 43. A spherical seat rod end 96 is attached to the forward end ofthe link and the rod end 96 in turn is connected to the ball socket 43.The actual axis of pivot of the rod end is selected so that the link 94forms a parallel link member with the stub shaft 77. The lever 93A inturn has another link 98 attached thereto with suitable rod ends, andthe opposite end of the link 98 is connected to an actuator lever 100adjustably connected to a shaft 101 which is an actuator shaft forchanging the setting (moving the wiper) of the potentiometer 89.

If the circle frame at the end of the drawbar 75, which is shown in FIG.I, is raised, for example, this will cause the entire drawbar assemblyto pivot about the horizontal pivot axis 102 of the ball 76 at the endof the stub shaft 77. Also, there will be no immediate pivoting of theshafts 79 because the cylinder 83 does not initially move, so the entiredrawbar acts like a rigid link across the junction with the stub shaft77.

Any movement of the drawbar aboutaxis 102 will also cause the link 94 topivot about its rod ends 95 and 96. The pivoting movement of the rod 94will result in pulling on the lever 93A because the link 94 does notchange in length. This will cause lever 93A to pivot about the axis ofshaft 93. Pivoting of the lever 93A pulls on the link 98, which in turn,causes the lever 100 to move and turn the shaft 101. As soon as thepotentiometer is moved off center the valve control circuitry for theservo valve 87 is powered and the valve directs fluid under pressure tothe cylinder 83 in a proper direction to extend pressure to the cylinder83 in a proper direction to extend the rod 85 until the parallelogramformed by the stub shaft 77 and the rod 94 returns to its originalposition. The center distances between the axis 102 and the horizontalpivot axis of rod end 95, and the center distance between the pivot axisof rod end 96, and the pivot axis of shaft 79, return to their originalrelationship. The movement of the lever 78 by the cylinder 83 restoresthe parallelogram, thereby moving link 98, arm 100 and shaft 101 towardtheir original positions until the potentiometer or servo valve controlreturns to its null position. The action is a continuous followingaction by cylinder 83 to keep the proper relationship of the link. Whenthe potentiometer is in null position, the circle frame drawbar 75 willbe level but may be at a changed height in relation to the ground. Thismeans that the circle frame attached to the drawbar 75 will also belevel and the unit can operate as previously described.

If the cylinder 83 is set as shown in FIG. 7, and the circle frame islowered to increase the depth of cut of the blade, the rear portions ofthe drawbar will be lowered. The lowering of the rear part of thedrawbar and stub shaft 77 about the axis 101 will cause the lever 93A tobe moved rearwardly, or in other words, in a direction toward thepotentiometer 89 because the link 94 does not collapse. The rod end 95moves in an are about the pivot axis of rod end 96 while the controller89 moves on an are about pivot axis 102. Therefore the arm 100 willcause rotation of shaft 101 to energize the solenoid valve 87 so thatthe cylinder 83 is retracted, retracting rod 85 and pulling lever 78 ina counterclockwise direction as viewed in FIG. 7 at the same time thedrawbar is lowering. This will continue to occur until the potentiometer89 resumes a null position. This will be when the relationship of thestub shaft 77 and link 94 has again returned to their originalrelationship. For example, this position is one such as that shown inFIG. 8 where the drawbar 75 is at a lower setting than in FIG. 7, withrespect to the grader frame, but wherein the potentiometer 89 is back inits null position. The relationship between the pivot axis 102, thepivot of shaft 79, and the pivot axes of the rod ends 95 and 96 isrestored to the same relationship as that in FIG. 7. The diagonaldistance between the pivot axis 102 and the pivot axis of rod end 95 isthe same in both figures.

The potentiometer 89 can be any desired configuration. Suitablepotentiometers for electro-hydraulic servo valves are made by Honeywell,Inc., Minneapolis, Minn. The potentiometer may be used in connectionwith controlling input to a servo valve amplifier as shown, or may beused in a bridge circuit. Details of direct feedback hydraulic servosystems are well known and therefore not shown in detail. The unit makesa closed loop servo control system with the potentiometer and parallellinkage provides the feedback.

The stub shaft and link form parallel link members and the diagonaldistance relationship between the corners of these members is restoredto a desired relationship when the potentiometer is in its null orcenter position.

The simple pivoting link pivoting about a horizontal axis substantiallytransverse to the direction of movement of the grader provides a pivotjoint in the drawbar between the circle frame and the ball joint for thedrawbar and by controlling the angular relationship between the twoportions that come together at this pivot joint. The circle frame can beleveled in fore and aft direction with respect to a horizontal plane sothat the grader blade then may be rotated about its upright axis withoutchanging the slope of cut of the blade.

This makes the grader blade easier to control automatically with levelor slope sensing devices such as a pendulum sensor or the like.

What is claimed is:

1. In grading machines having an earth working blade, a circle framemember for mounting said blade for rotation about an upright axis, amain frame, and means for connecting said circle frame to said mainframe comprising a drawbar member attached at one end thereof to saidcircle frame, means between said circle frame and said main frame toraise and lower said circle frame and first pivot means attaching theother end of said drawbar member to said main frame, said drawbar memberincluding two drawbar portions, means forming a second pivot connectionbetween said drawbar portions adjacent the first pivot means, and havinga pivot axis generally transverse to the direction of movement of theroad grader, and means interconnecting the two pivoted drawbar portionsto control the angular relationship between the two pivoted drawbarportions to level said circle frame at different depth positions of saidcircle frame.

2. The combination specified in claim 1 wherein said two drawbarportions comprise a main portion and a link portion, a lever arm fixedlyattached to said link portion and extending outwardlytherefrom, and saidmeans to control the angular relationship comprising a hydrauliccylinder positioned between said lever arm and said main portion tocontrol the angular relationship between said link portion and said mainportion.

3. The combination specified in claim 1 wherein said means to controlthe angular relationship comprises mechanical means for adjusting theangular position between said two drawbar portions comprising a screwthreaded member attached to a first of said drawbar portions about asecond pivot axis, and attached to a second of said drawbar portionsthrough threadably adjustable means.

4. The combination specified in claim 3 wherein the points of attachmentof said screw thread member are positioned in a plane spaced from theaxis of pivot between said two drawbar portions.

5. The combination specified in claim 2 wherein said link portioncomprises a stub shaft member, and the connection between said mainframe and said drawbar comprises a ball attached to one end of saidlink, bearing means to pivotally mount said stub shaft member to themain portion of said drawbar about a substantially transverse axis withrespect to the direction of movement of said grader.

6. The combination of claim 5 and said means to control the angularrelationship further comprising a servo valve controlling said hydrauliccylinder, and a servo valve controller having an actuating lever, asecond link, means mounting a first end of said second link to said mainframe, and means mounting a second end of said second link to saiddrawbar so that said second link and stub shaft link form parallel linkmembers, means to connect said second end of said second link to saidactuator whereby movement of said drawbar tends to change the diagonaldistance relationship of the pivots of said stub shaft and second linkrespectively, said controller and servo valve and hydraulic cylinder indirection to tend to retain said relationship by pivoting said stubshaft about transverse axis of mounting the main portion of saiddrawbar.

7. In a road grader having a main frame, means for supporting said mainframe for movement along the earth surface, said main frame having aforward portion, an earth working blade, means to rotatably mount saidearth working blade with respect to said main frame including a drawbarconnecting said earth working blade to the forward portions of said mainframe, said drawbar comprising two portions, a first portion beingconnected to said main frame and a second portion being connected tosaid earth working blade, means to pivotally mount said two portionstogether about an axis substantially transverse to the direction ofmovement of said main frame, hydraulic cylinder means to control theangular relation of said two portions about said transverse axis withrespect to each other and thereby control the height of said secondportion with respect to the main frame, one end of said hydrauliccylinder means being attached to a first of said portions, and a secondend of said hydraulic cylinder means being attached to a second of saidportions, control means on said road grader for said hydraulic cylinder,means on said frame to sense changes of depth of cut of said workingearth blade, said means to sense controlling said control means toadjust said hydraulic cylinder means to change the relationship of saidtwo portions as a function of the changes in depth of cut of the earthworking blade.

8. The road grader of claim 7 wherein said means to sense comprises alink, means to mount said link on said main frame, at location otherthan the connection of the drawbar to the main frame, and wherein saidcontrol means includes an activatable element, said link being connectedto said element.

9. A drawbar leveler for a road grader having a main frame, a drawbar,means comprising a ball joint connection connecting said drawbar to theforward portion of the main frame of said road grader, a grader bladeand circle frame, means to connect the drawbar to the grader blade andcircle frame at a rear portion of the drawbar, said drawbar comprisingtwo sections between said circle frame and said ball joint including afirst section connected to the circle frame and a second sectionconnected to the ball joint, means forming a pivot between said firstand second sections about a substantially transverse axis adjacent theforward portion of said drawbar, lever means on one of said sections anda support on the other section, and means to control the angularrelationship of the two sections about said pivot comprising anextendable and retractable actuator connected between said lever meansand said support respectively, and control means on said road graderresponsive to changes in the vertical position of said circle frame tocontrol said actuator to thereby change the angle between said twosections about said pivot and the vertical position of the portion ofsaid first section adjacent said pivot with respect to said ball joint.

10. The combination of claim 9 wherein said control means includes aparallelogram linkage including a first link portion pivoted at itsopposite ends on the axes of movement of said second section and asecond link pivoted at a first end adjacent said frame and at a secondend with respect to said drawbar on means permitting the second link tomove parallel to said first link portion during pivoting of saiddrawbar, said control means further including means to sense changes inposition of said second end of said second link relative to said drawbaras the drawbar pivots when the vertical position of said circle frame ischanged.

11. The combination of claim 10 wherein said means to control theangular relationship between said drawbar sections comprises a hydrauliccylinder, a servo valve controlling said cylinder, and means to controlsaid servo valve including a movable feedback means sensitive to theposition of said second end of said second link to actuate the servovalve in direction to restore a desired relationship between the secondend of said second link and said drawbar.

12. In an earth working machine having an earth working blade, a drawbarmember, means to connect said earth working blade to said drawbar forrotation about an upright axis, means between said drawbar and said mainframe to raise and lower said earth working blade, first pivot meansattaching a leading end of said drawbar member to said main frame, saiddrawbar member including first and second drawbar portions, meansforming a second pivot connection between said drawbar portions adjacentthe first pivot means, said second pivot connection defining a pivotaxis generally transverse to the direction of movement of the earthworking machine, means interconnecting the two pivoted drawbar portionsto control the angular relationship between the two pivoted drawbarportions to level said drawbar at different depth positions of saidearth working blade, and servo control means including a feedback sensorto control the means interconnecting the pivoted drawbar portions tomaintain one of said drawbar portions at a reference relationship withrespect to the main frame.

13. In an earth working machine having a main frame and an earth workingblade, means mounting said blade for rotation about a substantiallyupright axis for rotational movement in a generally horizontal planeincluding a drawbar member and having two portions, said means mountingsaid blade to said main frame having a first pivot connection to saidmain frame and a second pivot connection between said two portions ofsaid means mounting said blade, means interconnecting said two portionsto control the position of said two portions to maintain said bladeoriented for rotation substantially in a horizontal plane regardless ofchanges of depth of cut of said blade, and control means for said meansinterconnecting said two portions including a servo system having afeedback sensor to sense deviation of said blade from its desiredorientation and for operating said means interconnecting said twoportions portion to return said blade in its desired orientation.

1. In grading machines having an earth working blade, a circle framemember for mounting said blade for rotation about an upright axis, amain frame, and means for connecting said circle frame to said mainframe comprising a drawbar member attached at one end thereof to saidcircle frame, means between said circle frame and said main frame toraise and lower said circle frame and first pivot means attaching theother end of said drawbar member to said main frame, said drawbar memberincluding two drawbar portions, means forming a second pivot connectionbetween said drawbar portions adjacent the first pivot means, and havinga pivot axis generally transverse to the direction of movement of theroad grader, and means interconnecting the two pivoted drawbar portionsto control the angular relationship between the two pivoted drawbarportions to level said circle frame at different depth positions of saidcircle frame.
 2. The combination specified in claim 1 wherein said twodrawbar portions comprise a main portion and a link portion, a lever armfixedly attached to said link portion and extending outwardly therefrom,and said means to control the angular relationship comprising ahydraulic cylinder positioned between said lever arm and said mainportion to control the angular relationship between said link portionand said main portion.
 3. The combination specified in claim 1 whereinsaid means to control the angular relationship comprises mechanicalmeans for adjusting the angular position between said two drawbarportions comprising a screw threaded member attached to a first of saiddrawbar portions about a second pivot axis, and attached to a second ofsaid drawbar portions through threadably adjustable means.
 4. Thecombination specified in claim 3 wherein the points of attachment ofsaid screw thread member are positioned in a plane spaced from the axisof pivot between said two drawbar portions.
 5. The combination specifiedin claim 2 wherein said link portion comprises a stub shaft member, andthe connection between said main frame and said drawbar comprises a ballattached to one end of said link, bearing means to pivotally mount saidstub shaft member to the main portion of said drawbar about asubstantially transverse axis with respect to the direction of movementof said grader.
 6. The combination of claim 5 and said means to controlthe angular relationship Further comprising a servo valve controllingsaid hydraulic cylinder, and a servo valve controller having anactuating lever, a second link, means mounting a first end of saidsecond link to said main frame, and means mounting a second end of saidsecond link to said drawbar so that said second link and stub shaft linkform parallel link members, means to connect said second end of saidsecond link to said actuator whereby movement of said drawbar tends tochange the diagonal distance relationship of the pivots of said stubshaft and second link respectively, said controller and servo valve andhydraulic cylinder in direction to tend to retain said relationship bypivoting said stub shaft about transverse axis of mounting the mainportion of said drawbar.
 7. In a road grader having a main frame, meansfor supporting said main frame for movement along the earth surface,said main frame having a forward portion, an earth working blade, meansto rotatably mount said earth working blade with respect to said mainframe including a drawbar connecting said earth working blade to theforward portions of said main frame, said drawbar comprising twoportions, a first portion being connected to said main frame and asecond portion being connected to said earth working blade, means topivotally mount said two portions together about an axis substantiallytransverse to the direction of movement of said main frame, hydrauliccylinder means to control the angular relation of said two portionsabout said transverse axis with respect to each other and therebycontrol the height of said second portion with respect to the mainframe, one end of said hydraulic cylinder means being attached to afirst of said portions, and a second end of said hydraulic cylindermeans being attached to a second of said portions, control means on saidroad grader for said hydraulic cylinder, means on said frame to sensechanges of depth of cut of said working earth blade, said means to sensecontrolling said control means to adjust said hydraulic cylinder meansto change the relationship of said two portions as a function of thechanges in depth of cut of the earth working blade.
 8. The road graderof claim 7 wherein said means to sense comprises a link, means to mountsaid link on said main frame, at location other than the connection ofthe drawbar to the main frame, and wherein said control means includesan activatable element, said link being connected to said element.
 9. Adrawbar leveler for a road grader having a main frame, a drawbar, meanscomprising a ball joint connection connecting said drawbar to theforward portion of the main frame of said road grader, a grader bladeand circle frame, means to connect the drawbar to the grader blade andcircle frame at a rear portion of the drawbar, said drawbar comprisingtwo sections between said circle frame and said ball joint including afirst section connected to the circle frame and a second sectionconnected to the ball joint, means forming a pivot between said firstand second sections about a substantially transverse axis adjacent theforward portion of said drawbar, lever means on one of said sections anda support on the other section, and means to control the angularrelationship of the two sections about said pivot comprising anextendable and retractable actuator connected between said lever meansand said support respectively, and control means on said road graderresponsive to changes in the vertical position of said circle frame tocontrol said actuator to thereby change the angle between said twosections about said pivot and the vertical position of the portion ofsaid first section adjacent said pivot with respect to said ball joint.10. The combination of claim 9 wherein said control means includes aparallelogram linkage including a first link portion pivoted at itsopposite ends on the axes of movement of said second section and asecond link pivoted at a first end adjacent said frame and at a secondend with respect to said draWbar on means permitting the second link tomove parallel to said first link portion during pivoting of saiddrawbar, said control means further including means to sense changes inposition of said second end of said second link relative to said drawbaras the drawbar pivots when the vertical position of said circle frame ischanged.
 11. The combination of claim 10 wherein said means to controlthe angular relationship between said drawbar sections comprises ahydraulic cylinder, a servo valve controlling said cylinder, and meansto control said servo valve including a movable feedback means sensitiveto the position of said second end of said second link to actuate theservo valve in direction to restore a desired relationship between thesecond end of said second link and said drawbar.
 12. In an earth workingmachine having an earth working blade, a drawbar member, means toconnect said earth working blade to said drawbar for rotation about anupright axis, means between said drawbar and said main frame to raiseand lower said earth working blade, first pivot means attaching aleading end of said drawbar member to said main frame, said drawbarmember including first and second drawbar portions, means forming asecond pivot connection between said drawbar portions adjacent the firstpivot means, said second pivot connection defining a pivot axisgenerally transverse to the direction of movement of the earth workingmachine, means interconnecting the two pivoted drawbar portions tocontrol the angular relationship between the two pivoted drawbarportions to level said drawbar at different depth positions of saidearth working blade, and servo control means including a feedback sensorto control the means interconnecting the pivoted drawbar portions tomaintain one of said drawbar portions at a reference relationship withrespect to the main frame.
 13. In an earth working machine having a mainframe and an earth working blade, means mounting said blade for rotationabout a substantially upright axis for rotational movement in agenerally horizontal plane including a drawbar member and having twoportions, said means mounting said blade to said main frame having afirst pivot connection to said main frame and a second pivot connectionbetween said two portions of said means mounting said blade, meansinterconnecting said two portions to control the position of said twoportions to maintain said blade oriented for rotation substantially in ahorizontal plane regardless of changes of depth of cut of said blade,and control means for said means interconnecting said two portionsincluding a servo system having a feedback sensor to sense deviation ofsaid blade from its desired orientation and for operating said meansinterconnecting said two portions portion to return said blade in itsdesired orientation.